Digital linear actuators (DLAs) and stepper motors typically incorporate a rotor in the form of a magnetic cylinder. During calibration of the rotor, the flux density is measured (in Gauss), to determine the capacity of the rotor. Typical methods used to determine the flux density involve spinning the rotor at a predetermined high velocity (such as 1800 rpm), in a generated voltage fixture device required for screw-in family rotors. A separate tool is required for other types of rotors. These are only applicable for measuring flux density during the production process because the fixture is not suitable to fit nonproduction stepper motor rotors, or rotors which have bearings attached.
Another diagnostic method involves spinning the rotor assembly at high velocity, such as 1800 rpm, while assembled within the DLA. This method is an intrusive test method and degrades functionality of the DLA. The rotational speed required to develop generated voltage from the motor is sufficient to predicate degradation of internal bearings or lubricants. Insertion of the threaded shaft adaptor may damage the internal lead screw thread. The flux density in millitesla (mT) is plotted as a sine wave as shown in FIG. 1. While the plot shown in FIG. 1 shows the different flux density measurements, the plot in FIG. 1 is difficult to interpret, and provides no correlation between the flux density, and variations in the dimensions of the rotor.
Therefore, there exists a need for a method of measuring the flux density of a rotor used for a DLA or stepper motor during the development stages, which measures not only flux density, but also is capable of measuring surface irregularities of the rotor.